Implantable medical device incorporating miniaturized circuit module

ABSTRACT

Implantable medical devices (IMDS) having RF telemetry capabilities for uplink transmitting patient data and downlink receiving programming commands to and from an external programmer having an improved RF module configured to occupy small spaces within the IMD housing to further effect the miniaturization thereof. An RF module formed of an RF module substrate and at least one IC chip and discrete components has a volume and dimensions that are optimally minimized to reduce its volumetric form factor. Miniaturization techniques include: (1) integrating inductors into one or more IC chips mounted to the RF module substrate; (2) mounting each IC chip into a well of the RF module substrate and using short bonding wires to electrically connect bond pads of the RF module substrate and the IC chip; and (3) surface mounting discrete capacitors over IC chips to reduce space taken up on the RF module substrate. The integrated inductors are preferably fabricated as planar spiral wound conductive traces formed of high conductive metals to reduce trace height and width while maintaining low resistance, thereby reducing parasitic capacitances between adjacent trace side walls and with a ground plane of the IC chip. The spiral winding preferably is square or rectangular, but having truncated turns to eliminate 90° angles that cause point-to-point parasitic capacitances. The planar spiral wound conductive traces are further preferably suspended over the ground plane of the RF module substrate by micromachining underlying substrate material away to thereby reduce parasitic capacitances.

FIELD OF THE INVENTION

This invention relates generally to implantable medical devices (IMDs)having RF telemetry capabilities for uplink transmitting patient dataand downlink receiving programming commands to and from an externalprogrammer, and more particularly to a miniaturized circuit moduleconfigured to occupy a small space within the IMD housing to furthereffect the miniaturization thereof.

BACKGROUND OF THE INVENTION

A wide variety of IMDs that employ electronic circuitry for providingelectrical stimulation of body tissue and/or monitoring a physiologiccondition are known in the art. A number of IMDs of various types areknown in the art for delivering electrical stimulating pulses toselected body tissue and typically comprise an implantable pulsegenerator (IPG) for generating the stimulating pulses under prescribedconditions and at least one lead bearing a stimulation electrode fordelivering the stimulating pulses to the selected tissue. For example,cardiac pacemakers and implantable cardioverter-defibrillators (ICDs)have been developed for maintaining a desired heart rate during episodesof bradycardia or for applying cardioversion or defibrillation therapiesto the heart upon detection of serious arrhythmias. Other nerve, brain,muscle and organ tissue stimulating medical devices are also known fortreating a variety of conditions.

Currently available IMD IPGs including ICD and cardiac pacemaker IPGsare typically formed having a metallic housing that is hermeticallysealed and, therefore, is impervious to body fluids, a header orconnector assembly mounted to the housing for making electrical andmechanical connection with one or more leads, and possess telemetrycapabilities for communicating with external devices. Over the past 20years, ICD IPGs have evolved, as described in some detail in commonlyassigned U.S. Pat. No. 5,265,588, from relatively bulky, crude, andshort-lived ICD IPGs simply providing high energy defibrillation shocksto complex, long-lived, and miniaturized ICD IPGs providing a widevariety of pacing, cardioversion and defibrillation therapies. Numerousimprovements have been made in cardioversion/defibrillation leads andelectrodes that have enabled the cardioversion/defibrillation energy tobe precisely delivered about selected upper and lower heart chambers andthereby dramatically reducing the delivered shock energy required tocardiovert or defibrillate the heart chamber. Moreover, the high voltageoutput circuitry has been improved in many respects to providemonophasic, biphasic, or multi-phase cardioversion/defibrillation shockor pulse waveforms that are efficacious, sometimes with particularcombinations of cardioversion/defibrillation electrodes, in lowering therequired shock energy to cardiovert or defibrillate the heart.

Such ICD IPGs need to be small enough to be comfortably implantedsubcutaneously without being unduly uncomfortable to the patient orcosmetically apparent. The first implanted automatic implantabledefibrillator (AID) IPG housing disclosed in U.S. Pat. No. 4,254,775 wasvery large and had to be implanted in a patient's abdominal region.Since that time, the ICD IPGs have been reduced in size while theircomplexity has been vastly increased. Battery energy requirements forpowering both the low voltage integrated circuits (ICs) and forproviding the cardioversion/defibrillation shocks have been reducedwhile battery energy density has been increased and batteryconfiguration made more conforming to the interior space of the ICD IPGhousing. Miniaturized, flat high voltage output capacitors that can beshaped to fit the allocated housing space and miniaturized high voltageswitching components have been developed and employed. All of theseimprovements, together with the above-mentionedcardioversion/defibrillation improvements have contributed to asignificant reduction in the volume of the ICD IPG housing withoutsacrificing longevity and capabilities.

Similar improvements in reducing housing volume have been made in otherIMD IPGs, particularly implantable cardiac pacemakers, nerve stimulatorsand monitors, over the same time period. Remote programming andinterrogation of IMD operating modes and parameters has been implementedin the above-described IMDs employing uplink (from the IMD) and downlink(to the IMD) telemetry transmissions between an RF transceiver withinthe IMD and an external transceiver of an external “programmmer”. Suchprogrammers are used to program the IMD by downlink telemetrytransmission of commands that are received and stored in memoryincorporated within the IMD that change an operating mode or parametervalue governing a function performed by the IMD.

Both non-physiologic and physiologic data (collectively referred toherein as “patient data”) can be transmitted by uplink RF telemetry fromthe IMD to the external programmer. The physiologic data typicallyincludes stored and real time sampled physiologic signals, e.g.,intracardiac electrocardiogram amplitude values, and sensor outputsignals. The non-physiologic patient data includes currently programmeddevice operating modes and parameter values, battery condition, deviceID, patient ID, implantation dates, device programming history, realtime event markers, and the like. In the context of implantablepacemakers and ICDs, such patient data includes programmed senseamplifier sensitivity, pacing or cardioversion pulse amplitude, energy,and pulse width, pacing or cardioversion lead impedance, and accumulatedstatistics related to device performance, e.g., data related to detectedarrhythmia episodes and applied therapies.

The RF telemetry transmission system that evolved into current commonusage relies upon magnetic field coupling through the patient's skin ofan IMD IPG antenna with a closely spaced programmer antenna. Lowamplitude magnetic fields are generated by current oscillating in an LCcircuit of an RF telemetry antenna of the IMD or programmer in atransmitting mode. The currents induced in the closely spaced RFtelemetry antenna of the programmer or IMD are detected and decoded in areceiving mode. Short duration bursts of the carrier frequency aretransmitted in a variety of telemetry transmission formats. In theMEDTRONIC® product line, the RF carrier frequency is set at 175 kHz, andthe IMD RF telemetry antenna located within the IMD housing is typicallyformed of coiled wire wound about a bulky ferrite core.

Apart from the bulk of the antenna taking up valuable space within theIMD housing, there are a number of other limitations in the currentMEDTRONIC® telemetry system employing the 175 kHz carrier frequency.First, using a ferrite core, wire coil, RF telemetry antenna results ina very low radiation efficiency because of feed impedance mismatch andohmic losses and a radiation intensity attenuated proportionally to atleast the fourth power of distance (in contrast to other radiationsystems which have radiation intensity attenuated proportionally tosquare of distance). These characteristics require that the implantablemedical device be implanted just under the patient's skin and preferablyoriented with the RF telemetry antenna closest to the patient's skin sothat magnetic field coupling is provided. To ensure that the datatransfer is reliable, it is necessary for the patient to remain stilland for the medical professional to steadily hold the RF programmer headagainst the patient's skin over the IMD for the duration of thetransmission. The time delays between downlink telemetry transmissionsdepend upon the user of the programmer, and there is a chance that theprogrammer head will not be held steady. If the uplink telemetrytransmission link is interrupted by a gross movement, it is necessary torestart and repeat the uplink telemetry transmission.

Secondly, the RF telemetry data transmission rate is limited employing a175 kHz carrier frequency. As device operating and monitoringcapabilities multiply, it is desirable. to be able to transmit out everincreasing volumes of data in real time or in as short a transmissiontime as possible with high reliability and immunity to spurious noise.In an uplink telemetry transmission from an IMD, it is desirable tolimit the current drain from the implanted battery as much as possible,simply to prolong IMD longevity.

As a result of these considerations, IMD-programmer RF telemetry schemeshave been proposed having the objectives of eliminating the bulkyantenna within the IMD housing to conserve space, eliminating the needfor the close, steady magnetic field coupling to enable uplink anddownlink telemetry transmission at a greater distance, increasing thedata transmission rate, and minimizing battery consumption. It has beenproposed to replace the ferrite core, wire coil, RF telemetry antenna inthe IMD with an antenna that can be located outside the hermeticallysealed enclosure and to employ higher carrier frequencies and datatransmission rates. It is suggested that the RF telemetry antenna may belocated in the IPG header in U.S. Pat. No. 5,342,408. A further U.S.Pat. No. 4,681,111 suggests the use of a stub antenna associated withthe header as the IMD RF telemetry antenna for high carrier frequenciesof up to 200 MHz and employing phase shift keying (PSK) modulation. Theelimination of the need for a VCO and a bit rate on the order of 2-5% ofthe carrier frequency or 3.3-10 times the conventional bit rate arealleged. In commonly assigned U.S. Pat. No. 5,861,019, it is proposedthat the telemetry antenna be formed as a microstrip patch antenna thatis conformal with the exterior housing of the IMD. The uses of the204-216 MHz band and the 902-908 MHz ISM band have been proposed in U.S.Pat. Nos. 5,944,659 and 5,767,791 for telemetry transmissions betweenexternally worn patient monitors and fixed location networkedtransceivers for ambulatory patient monitoring in a hospital context.

In order to fit within a minimal space, all electronic circuits of theIMD circuitry are preferably formed as ICs, but implementation of RFtelemetry circuitry has required use of discrete capacitors andinductors mounted along with the RF IC to a circuit board. The use ofsuch discrete inductors and capacitors is not eliminated, but isactually increased, in the above-described high frequency, high datatransmission rate telemetry transceiver circuitry. The relocation of thebulky RF telemetry antenna to a less critical area outside thehermetically sealed IMD housing reduces space requirements. However, thediscrete inductor and capacitor components mounted with one or more ICchip to an RF IC module substrate render the RF module unduly large suchthat it occupies a substantial portion of the volume within the IMDhousing.

SUMMARY OF THE INVENTION

The present invention is directed to an IMD having a hermetically sealedchamber defined by a hermetically sealed housing, wherein the housinghas an inner and an outer wall surface of a predetermined contour andenclosing a housing cavity or chamber of a predetermined volume. Inaccordance with a basic aspect of the present invention, the circuitryof the IMD comprises at least one circuit module comprising an IC chipmounted on a substrate and one or more discrete capacitor and/ormicro-machined inductor that is/are selectively mounted directly orindirectly to the substrate in a manner reducing the volumetric formfactor of the resulting circuit module.

In accordance with one embodiment of the invention, an RF module formedof an RF module substrate and at least one IC chip and discretecomponents has a volume and dimensions that are optimally minimized toreduce its volumetric form factor. In a first aspect of the invention,inductors are integrated into one or more IC chips mounted to the RFmodule substrate. In a further aspect of the invention, discretecapacitors are surface mounted over IC chips to reduce space taken up onthe RF module substrate and to shorten the conductive paths between theIC and the capacitor. In a still further aspect of the invention, eachIC chip is mounted into a well of the RF module substrate and shortconductors are employed to electrically connect bond pads of the RFmodule substrate and the IC chip.

The inductors are preferably fabricated as planar spiral woundconductive traces formed of high conductive metals to reduce traceheight and width while maintaining low resistance, thereby reducingparasitic capacitances between adjacent trace side walls and with aground plane of the IC chip. The spiral winding preferably is square orrectangular, but having truncated turns to eliminate 90° angles thatcause point-to-point parasitic capacitances.

The planar spiral wound conductive traces are further preferablysuspended over the ground plane of the RF module substrate bymicromachining underlying substrate material away to thereby reduceparasitic capacitances.

In these ways the form factor of the RF module is decreased, and thespace within the IMD housing can be occupied by other components or canresult in making the housing itself smaller and possibly thinner inprofile than it would otherwise be. The form factor of other circuitmodules of the IMD circuitry can also be reduced by employing the sametechniques.

This summary of the invention and the objects, advantages and featuresthereof have been presented here simply to point out some of the waysthat the invention overcomes difficulties presented in the prior art andto distinguish the invention from the prior art and is not intended tooperate in any manner as a limitation on the interpretation of claimsthat are presented initially in the patent application and that areultimately granted.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the invention will becomeapparent to those skilled in the art from the following detaileddescription of a preferred embodiment, especially when considered inconjunction with the accompanying drawings in which:

FIG. 1 is a simplified schematic view of an ID constituting a cardiacpacemaker or ICD and an external programmer employing the improved RFtelemetry antenna of the present invention;

FIG. 2 is a simplified block diagram of major functional uplink anddownlink telemetry transmission functions of the external programmer andIMD of FIG. 1;

FIG. 3 is a simplified block diagram of the transceiver components ofthe IMD of FIG. 1;

FIG. 4 is a schematic circuit of the RF module of FIG. 3;

FIGS. 5A and 5B are side and bottom views, respectively of the physicallayout and size of the RF module of FIGS. 3 and 4 employing conventionaldiscrete inductors and capacitors defining a volumetric form factor;

FIGS. 6A and 6B are side and bottom views, respectively of the physicallayout and size of the RF module of FIGS. 3 and 4 employing ICfabricated inductors, IC mounted capacitors and particular IC mountingtechniques of the present invention defining a reduced sized volumetricform factor;

FIG. 7 is a schematic illustration of a spiral wound inductor formed byIC fabrication processes on the RF IC;

FIG. 8 is a partial cross-section view taken along lines 8—8 of FIG. 7illustrating fabrication of the traces forming the spiral turns of thespiral inductor of FIG. 7;

FIG. 9 is a partial cross-section view taken along lines 9—9 of FIG. 7illustrating fabrication of the traces forming the spiral turns of thespiral inductor of FIG. 7 suspended on a platform; and

FIG. 10 is a side view in partial cross-section showing the mounting ofthe RF IC in a well of the RF module substrate and a discrete capacitorsurface mounted to the RF IC surface.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

The present invention can be implemented in any IMD having highfrequency RF telemetry capabilities. The present invention will bedescribed in relation to a cardiac pacemaker or ICD IPG operating systemdesign, but it is not intended that the invention be limited to thatparticular application when it can be advantageously implemented invarious types of IMDs. At present, a wide variety of IMDs arecommercially released or proposed for clinical implantation. Suchmedical devices include implantable cardiac pacemakers as well as ICDs,pacemaker-cardioverter-defibrillators, drug delivery pumps,cardiomyostimulators, cardiac and other physiologic monitors, nerve andmuscle stimulators, deep brain stimulators, cochlear implants,artificial hearts, etc. As the technology advances, IMDs become evermore complex in possible programmable operating modes, menus ofavailable operating parameters, and capabilities of monitoringincreasing varieties of physiologic conditions and electrical signalswhich place ever increasing demands on the telemetry transmissionsystem.

FIG. 1 illustrates bidirectional telemetry communication between anexternal programmer 26 and an IMD, e.g., an ICD or cardiac pacemaker IPG12, in accordance with the present invention. The IPG 12 is implanted inthe patient 10 beneath the patient's skin or muscle and is typicallyoriented to the skin surface. The IPG 12 is electrically coupled to theheart 18 of the patient 10 through pace/sense orcardioversion/defibrillation electrodes and lead conductor(s) of atleast one endocardial lead 14 coupled to the IPG connector in a mannerknown in the art. The IPG 12 contains a battery and an operating systempowered by the battery that may employ a microcomputer or a digitalstate machine for timing and controlling device functions in accordancewith a programmed operating mode. The operating system includes memoryregisters in RAM for storing a variety of programmed-in operating modeand parameter values that are used by the operating system. The memoryregisters may also be used for storing data compiled from sensed cardiacactivity and/or relating to device operating history or sensedphysiologic parameters for telemetry out on receipt of a retrieval orinterrogation instruction.

When the IPG 12 is a cardiac pacemaker or is an ICD including pacingcomponents, its operating system also includes sense amplifiers fordetecting cardiac signals, pulse generating output circuits fordelivering pacing pulses to at least one heart chamber of the heart 18,and optionally includes patient activity sensors or other physiologicsensors for sensing the need for cardiac output and modulating pacingparameters accordingly in a manner well known in the prior art. When theIPG 12 is an ICD, it includes one or more high powercardioversion/defibrillation output capacitor, electronic circuitrycoupled to the sense amplifiers for detecting and discriminatingpathologic and/or non-pathologic arrhythmias from one another andproviding other functions, high voltage electronic charging circuitryfor charging the output capacitor(s) from a battery voltage to a highervoltage, and electronic switching circuitry for dumping the charge builtup on the output capacitor(s) through the cardioversion/defibrillationelectrodes. Such a pacing or ICD IPG 12 is described in detail incommonly assigned U.S. Pat. No. 5,626,620 or U.S. Pat. No. 5,931,857,respectively.

The IPG operating system also includes telemetry circuitry and atelemetry antenna 28, which typically include relatively bulky discretecomponents described further below. The IPG telemetry antenna 28 cantake the form of a surface mounted antenna described in theabove-referenced '019 patent or an antenna enclosed within or mounted tothe IPG connector. The physical space within the IPG housing is limited,and it is desirable to reduce the size of components fitting within iteither to reduce the overall size and weight of the IPG 12 or toincrease the battery size to increase longevity. In accordance with thepresent invention, the size of discrete components of the RF module ofthe IPG circuitry is decreased to accomplish that goal. By way ofbackground to place this in context, the IPG telemetry system andfunctions are first described as follows.

Programming commands or data are transmitted between the IPG RFtelemetry antenna 28 within or on a surface of the IPG 12 and anexternal RF telemetry antenna 24 associated with the external programmer26. Preferably, a high frequency carrier signal in the range of 402 to405 MHz is employed and it is not necessary that the external RFtelemetry antenna 24 be contained in a programmer RF head so that it canbe located close to the patient's skin overlying the IPG 12. Instead,the external RF telemetry antenna 24 can be located on the case of theexternal programmer some distance, e.g., about two to five meters, fromthe patient 10. For example, the external programmer 26 and external RFtelemetry antenna 24 may be on a stand a few meters or so away from thepatient 10 as described, for example, in the above-referenced '019patent and in commonly assigned U.S. Pat. Nos. 5,683,432 and 5,843,139.Moreover, the patient 10 may be active and could be exercising on atreadmill or the like during an uplink telemetry interrogation of realtime ECG or physiologic parameters. The programmer 26 may also bedesigned to universally program existing IPGs that employ theconventional ferrite core, wire coil, RF telemetry antenna of the priorart and therefore also have a conventional programmer RF head andassociated software for selective use with such IPGs.

In an uplink telemetry transmission 20, the external RF telemetryantenna 24 operates as a telemetry receiver antenna, and the IPG RFtelemetry antenna 28 operates as a telemetry transmitter antenna.Conversely, in a downlink telemetry transmission 22, the external RFtelemetry antenna 24 operates as a telemetry transmitter antenna, andthe IPG RF telemetry antenna 28 operates as a telemetry receiverantenna.

FIG. 2 illustrates certain of the functional telemetry transmissionblocks of the external programmer 26 and IPG 12 of FIG. 1. The externalRF telemetry antenna 24 within the programmer 26 is coupled to atelemetry transceiver comprising a telemetry transmitter 32 andtelemetry receiver 34. The programmer telemetry transmitter 32 andtelemetry receiver 34 are coupled to control circuitry and registersoperated under the control of a microcomputer and software as describedin commonly assigned U.S. Pat. No. 5,843,139, for example. Similarly,within the IPG 12, the IPG RF telemetry antenna 28 is coupled to atelemetry transceiver comprising a telemetry transmitter 42 andtelemetry receiver 44 incorporated into an RF module 50 that is furtherdescribed below with reference to FIGS. 3 and 4.

In an uplink telemetry transmission 20, the telemetered data may beencoded in any of the telemetry formats. In a particular exampledescribed below, the data encoding or modulation is in the form offrequency shift key (FSK) modulation of the carrier frequency, forexample. To initiate an uplink telemetry transmission 20, the telemetrytransmitter 32 in external programmer 26 is enabled in response to auser initiated INTERROGATE command to generate an INTERROGATE command ina downlink telemetry transmission 22. The INTERROGATE command isreceived and demodulated in receiver 44 and applied to an input of theIMD central processing unit (CPU), e.g. a microcomputer (not shown). TheIMD microcomputer responds by generating an appropriate uplink datasignal that is applied to the transmitter 42 to generate the encodeduplink telemetry signal 20.

A simple bit stream format is employed that can be used to robustlytransmit INTERROGATE commands or PROGRAM instructions under the controlof a programmer CPU. Each RF pulse of the INTERROGATE instruction orcommand that is transmitted in the downlink telemetry transmission 22causes the IPG antenna receiver 44 to ring. The train of inducedvoltages is detected and decoded by the receiver 44. After theINTERROGATE command or instruction is decoded, the stored data to beuplink transmitted is encoded into PPM modulated RF pulses in dataframes, for example. The IPG transmitter 42 applies voltage to the IPGRF antenna 28 to generate the uplink RF pulses which are transmittedthrough the patient's body and the intervening air to the external RFtelemetry antenna 24. The transmitted signals are detected in thetelemetry receiver 34 and applied as a pulse train to further decodingcircuitry to decode the transmitted data so that at the data can berecorded or displayed as described above.

The uplink and downlink telemetry transmissions follow a telemetryprotocol that formulates, transmits and demodulates data packets eachcomprising a bit stream of FSK modulated data bits. A carrier frequencycentered in a 300 kHz band between 402 MHz and 405 MHz is modulated infrequency or frequency shifted up representing a data bit “1” or “0” orshifted down to represent the other data bit. The data packets areformulated of an FSK data bit stream with a preamble, data and errorchecking data bits.

FIG. 3 further schematically depicts the IPG telemetry circuitry whichis embodied in the RF module 50 and the IMD system module 60. The RFtelemetry module 50 is physically embodied in a miniaturized circuitboard 56 on which are mounted the RF IC chip 52, the electronic control(ETC) chip 54, a number of discrete components described further below,bonding pads and conductors formed on the surface of the circuit board56. Electrical connections are made between certain of the bonding padsand the IMD system module 60 or a feedthrough pin (not shown) extendingthrough the IPG housing wall (not shown) and coupled to the IPG RFantenna 28. The IMD system module 60 similarly is embodied in aminiaturized circuit board 66 on which are mounted at least one IMDsystem chip 62, telemetry digital hardware interface 64, a number ofdiscrete components, and deposited bonding pads and conductors formaking electrical connections therebetween and with further componentsof the IMD which play no role in the present invention. The printedcircuit boards or substrates 56 and 66 are formed in the typical mannersof epoxy-glass and polyamide flex printed wiring boards, ceramic orsilicon substrates including employing silicon wafer scale integrationtechniques.

The hardware interface 64 comprises uplink and downlink RAM buffers,control and status registers, and interrupt lines as well as asynchronous serial bus, transmit and receive serial data lines, afrequency standard input to the phase detector and AFC control lines.The hardware interface 64 includes a baseband receiver signal processor,a protocol physical layer controller, a CPU, and RAM and functions asthe RF module controller and interface. In the receive mode, thebaseband receiver signal processor implements an AFC frequency controlof the VCO and provides bit synchronization and demodulation functionsfrom the received data bit stream of each packet so that the receiveddata is demodulated without errors. The protocol physical layercontroller functions to detect the preamble of the packet and to performCRC processing of the CRC data bits of the packet for both the transmitand receive operations.

FIG. 4 depicts the circuitry of the RF module 50 including the RF ICchip 52, the ETC chip 54 and the discrete components that provide thefunctions of a “Zero IF” receiver 44, an FSK transmitter 42, a UHFFrequency Synthesizer providing both local oscillator injection to theUHF receiver's UHF Mixers, and a Frequency Shift Key (FSK) FM carrierfor the FSK transmitter 42. In a″ downlink telemetry receive mode,INPHASE (I) and QUADRATURE (Q) baseband IF signals are developed by theRF Mixers in the RF IC chip 52 that are forwarded for digitaldemodulation and bit sync and signal processing by the telemetry digitalhardware 64. In an FSK uplink telemetry transmit mode, TX DATA isencoded in ETC chip 54 and uplink telemetered by FSK modulation of thecarrier signal developed by a voltage controlled oscillator (VCO)resident in part on the RF IC chip 52 and in a tank circuit formed ofdiscrete inductor L1, capacitor C1 and diode D1.

The ETC chip 54 is a mixed signal chip that provides a phase detector,charge pump, lock detector and programmable counters of the frequencysynthesizer, an FSK modulator, an AFC control, current DACs for setup ofthe RF IC chip 52, and a controller interface. The discrete componentsof the RF module 50 include the phase lock loop (PLL) loop filtercapacitor C1, inductor L1, tuning varactor diode D1, a surface acousticwave resonator SAW, and an antenna transmit/receive switch T/R. Inaddition, further discrete inductors L2, L3, L4 and capacitors C2, C3,C4, C5, C6 are required for proper circuit functions coupled to theantenna 28 directly or through the transmit/receive switch T/R or to theSAW. Additionally, mutually coupled inductors, in the form oftransformers, can be used as baluns to drive balanced circuits and alsoto provide direct and broadband impedance transformations. Thetransformer function could be used for driving diode bridges in balancedmixers and impedance matching from 50 ohm unbalanced impedances (i.e.,antennas) to the higher, balanced, impedances present in low current RFICs.

In the prior art, these discrete components L1-L4 and C1-C6 would beelectrically mounted on the RF module substrate 56 and connected to padsof the RF IC 52 or the ETC IC 54 or to other discrete components mountedto the RF module substrate 56 as shown, for example, in FIGS. 5A and 5B.The small value discrete inductors L1-L5 (from 5 to 45 nanoHenries) musthave very high quality factors (or Q) that are greater than or equal to60 at the carrier frequency f_(c) and L values. These requirements havedictated the use of discrete wire wound, air core inductors that havethe requisite inductance and Q and that are bonded to bonding pads ofthe RF module substrate 56.

Similarly, the small value capacitors (from 0.5 to 39 pF) must have Qsin excess of 150 at the carrier frequency f_(c). Chip capacitors raiseinductance issues with present interconnect methods (i.e., substratetraces, and wire bonds). Typically, the capacitor values are chosen toseries resonate with the wirebond/trace inductance. This often requiresmultiple capacitors for effectively providing broadband bypassing toground. If the inductance is minimized, the self-resonant frequency ofthe capacitor can be raised high enough to minimize this effect.

It is conventional practice to mount discrete capacitors to bonding padson the surface of the RF module substrate 56. But, such mountingrequires substrate conductors extending from the bonding pads to bondingpads adapted to be electrically connected to IC bonding pads byconductors that bridge the physical gap. Parasitic capacitances developbetween such substrate conductors and bridging conductors and adjacentconductors and the substrate ground plane that must be compensated for.

Moreover, the provision of the bonding pads and conductive traces fromthe bonding pads to other bonding pads on a surface of the RF modulesubstrate 56 increases the overall length and width of the RF modulesubstrate 56 to provide the surface real estate. The discrete capacitorsand inductors are typically packaged in a hexahedral form having apackage length and width defining the surface mount area and a heightextending from a surface mounting or floor side and the free or roofside. The three-dimensions and the resulting hexahedral envelope volumeis referred to as a “form factor” of the RF module 50. The RF moduleform factor is therefore dictated by the number, sizes and requiredspacing of these discrete inductors and capacitors, other discretecomponents described above, the RF IC chip 52 and ETC IC chip 54, edgebonding pads for connection with IMD system module 60 and the battery,and the conductors or conductive traces electrically connecting themtogether.

FIGS. 5A and 5B depict such a three dimensional RF module 50 having aplurality of discrete inductors, capacitors and ICs mounted to andprojecting from the top and bottom surfaces of the RF module substrate56 following conventional surface mount fabrication processes that aremodified following the teachings of the present invention. The inductorsL1-L5 project outward the furthest from the top and bottom surfaces ofRF module substrate 56 and thereby define the overall thickness of theform factor 61 defining the spatial volume occupied within the IMDhousing sealed chamber. Moreover, the locations of the inductors L1-L5against the top and bottom surfaces of RF module substrate 56 spacedaway from the RF IC chip 52 and the ETC chip 54 consume surface area or“real estate” of the top and bottom surfaces of RF module substrate 56,thereby increasing its overall length and width and the correspondinglength and width dimensions of the hexahedral form factor 61.

Similarly, the discrete capacitors C1-C6 are surface mounted and coupledto bonding pads on the top and bottom surfaces of RF module substrate 56spaced away from the RF IC chip 52 and the ETC chip 54. These substratesurface mounts also consume real estate of the top and bottom surfacesof RF module substrate 56, thereby increasing its overall length andwidth and the corresponding length and width dimensions of thehexahedral form factor 61.

Additionally, the RF IC chip 52 and ETC chip 54 are surface mounted andcoupled to bonding pads on the top and bottom surfaces of RF modulesubstrate 56 spaced away from the RF IC chip 52 and the ETC chip 54..The substrate surface mounting of the IC chips cause the IC chips toproject outward and lengthens the conductors extending between exposedsurface IC chip bonding pads and bonding pads on the RF module substrate56. Such elevated and lengthened conductors increase parasiticcapacitances and inductances.

The present invention involves integration of the inductors into the RFIC chip 52 and/or the ETC chip 54 to effectively eliminate the discreteinductors and thereby reduce the height and volume of the RF module asshown in the three dimensional RF module 50 depicted in FIGS. 6A-6B. Inthis illustrated example, the inductors L1-L3 are incorporated into RFIC chip 52, and capacitors C1-C3 are mounted to RF IC chip 52. CapacitorC6 is mounted to ETC chip 54, and a discrete IC is provided for inductorL4 to provide for ready connection with the T/R switch. Alternatively,at least inductor L1 and capacitor C1 could be incorporated into ormounted onto ETC chip 54.

According to conventional practice in IMD design and fabrication,inductors are not presently integratable into an IC due to a high valueof parasitic capacitance to the substrate as Q_(p)=Rp/(2*Pl*f*L) whereRp (parallel resistance) is due to intrinsic substrate conductivity.Another limiting factor in inductor Q is Rs or series resistance asQ_(s)=(2*PI*f*L)/Rs. Series resistance, in this case, is primarily dueto effective conductivity of the inductor's conductor (with skin effectand surface roughness effects included). Both effects must be includedin determining the actual Q for the inductance(Q_(actual)=1/((1/Q_(s))+(1/Q_(p))).

However, it is feasible to fabricate certain of the high Q inductors byintegration of inductors onto the surface of an ASIC IC, e.g., RF IC 52and/or ETC IC 54, if certain design features and fabrication techniquesare employed. Referring to FIG. 7, first, the design of the inductor 70is in the shape of a planar spiral 72 formed on IC surface 78 extendingbetween bonding pads 74 and 76 coupled to first and second ends of theplanar spiral 72. The first end of the planar spiral 72 is coupledthrough a via to a conductive trace disposed below the IC surface 78 andextending laterally across the planar spiral 72 and is in turn coupledto the bonding pad 74 by way or a further via. These fabricationtechniques are described, for example, in “RF Circuit design Aspects ofSpiral Inductors on Silicon”, Burghartz, et al., IEEE Journal ofSolid-State Circuits, Vol 33, No. 12, December, 1998, pp. 2028-34 and inU.S. Pat. Nos. 5,793,272, 5,884,990, 6,054,329, 6,114,937, and5,416,356.

The spiral turns of planar spiral 72 are arranged around an open centralarea 79 because tightly wound centrally disposed spirally wound centralturns add significant resistance R without contributing any appreciableinductance L. Furthermore, the planar spiral 72 is implemented withdiagonal corners to minimize impedance mismatch (and thus energy losses)of a right angle design.

The spiral turns are deposited as a continuous trace 82 on IC surface 78or as a layer of IC substrate 80 preferably using a high conductivityconductor selected from the group consisting of gold, copper oraluminum-copper metallization instead of standard aluminum or aluminumsilicide metallization. Copper has less than one-half the impedance ofsimilar thickness aluminum. Therefore the thickness or wall height ofthe traces can be reduced as shown in FIG. 8 from the dotted linethickness t₂ to the solid line thickness t₁. The reduction in thicknessor trace wall height using copper metallization also reduceswall-to-wall parasitic capacitance by one-half. Moreover, parasiticcapacitance across IC substrate 80 to an underlying conductive groundplane 84 may be reduced 30% because the track width t_(w) may be reducedto 70% of an equivalent aluminum track width twa at the same impedancelevel.

Substrate capacitance of the inductor is additionally substantiallyreduced by the implementation of the spiral inductor 70 on amicromachined (MEM) platform 86 as shown in FIG. 9. Additionally, a SOIsubstrate should optimally be used. A segmented ground plane 84 mayoptionally be added. The SOI substrate 80 is etched to a thin platform86 by back etching as is known in the art and described, for example, in“Suspended SOI Structure for Advanced 0.1 μm CMOS RF Devices”, Hisamoto,et al., IEEE Transactions on Electron Devices, Vol 45, No. 5, May 1998,pp. 1039-46. Leaving the thin platform 86 in place rather than fullyetching the silicon substrate away makes the planar spiral 72 morereadily producible and robust. However, it will be understood that theplanar spiral 72 could be fully suspended without a planar support.

Additionally, chip inductor and capacitor integration may beaccomplished by using “wafer scale integration” techniques wherebycapacitor (or inductor) contact areas are integrated onto the surface ofa RF IC 52. FIG. 10 shows that the RF IC 52 is placed. in a well 88 ofthe RF module substrate 56, and that a discrete capacitor 90 is fittedover it. The small chip capacitor 90 (such as 68 pF 0.01×0.01″Dielectric Labs, Inc., Part No. D10) can be soldered or epoxy attacheddirectly to the surface 78 of the RF IC 52. This direct IC mountingeliminates substantial parasitic high frequency impedance, capacitanceand/or inductance caused by IC routing to the edge of the die, wirebonds to the supporting substrate, substrate interconnect to substratepads and substrate pads and allows the capacitors to be reduced in size.The capacitor body may be placed over active IC functional circuitry tofurther reduce die area. Additionally the RF IC 52 may be placed in awell 57 within RF module substrate 56 over substrate ground plane 59 tominimize the length of wire bond wires 92 and thereby reducing parasiticcapacitance and inductance occasioned by longer wires required when theRF IC 52 is surface mounted to substrate 56.

Utilizing these fabrication techniques advantageously reduces the formfactor (i.e., size, volume) of all the circuitry of the RF module 50,minimizes substrate noise and/or coupling, improves performance, reducesfully allocated product costs (FAPC), and does not introduce anysubstantial packaging issues. Standard wafer fabrication processes canalso be economically employed. Further articles relating to fabricationprocesses that can be employed include: “Micromachined Planar SpiralInductor in Standard GaAs HEMT MMIC Technology”, Ribas, et al., IEEEElectron Device Letters, Vol. 19, No. 8, August 1998, pp. 285-7;“Analysis, Design, and Optimization of Spiral Inductors and Transformersfor Si RF IC's”, Niknejad, et al., IEEE Journal of Solid-State Circuits,Vol 33, No. 10, October 1998, pp. 1470-81; “A Novel High-Q andWide-Frequency-Range Inductor Using Si 3-D MMIC Technology”, Kamogawa,et al., IEEE Microwave and Guided Wave Letters, Vol 9, No. 1, January1999, pp. 16-18; “Integrated Circuit Technology Options forRFIC's—Present Status and Future Directions”, Larson, IEEE Journal ofSolid-State Circuits, Vol 33, No. 3, March 1998, pp. 387-99; and“Micromachined Electro-Mechanically Tunable Capacitors and TheirApplications to RF IC's”, Dec et al., IEEE Transactions on MicrowaveTheory and Techniques, Vol 46, No. 12, December 1998, pp. 2587-95.

All patents and other publications identified above are incorporatedherein by reference.

While the present invention has been illustrated and described withparticularity in terms of preferred embodiments, it should be understoodthat no limitation of the scope of the invention is intended thereby.The scope of the invention is defined only by the claims appendedhereto. It should also be understood that variations of the particularembodiments described herein incorporating the principles of the presentinvention will occur to those of ordinary skill in the art and yet bewithin the scope of the appended claims.

What is claimed is:
 1. An implantable medical device operable to performa therapeutic and/or monitoring function comprising: a housing having ahousing side wall and inner and outer wall surfaces of a predeterminedcontour enclosing a hermetically sealed chamber; and a battery enclosedwithin said hermetically sealed chamber; an electronic circuit modulepowered by the battery comprising a plurality of discrete components andat least one integrated circuit IC chip mounted to a circuit boardhaving a volumetric form factor dimensioned to fit within saidhermetically sealed chamber along with said battery, said electroniccircuit module comprising at least one micromachined IC inductor formedintegrally with said IC chip thereby reducing the form factor of theelectronic circuit module.
 2. The implantable medical device of claim 1,wherein the IC inductor comprises a planar spiral formed of acontinuous, conductive, spiral trace extending between bonding pads thatis deposited as a layer of the IC chip substrate, the spiral tracehaving turning points that are angled at less than 90° to reduceparasitic capacitance between adjacent turning points of the spiraltrace.
 3. The implantable medical device of claim 1, wherein the ICinductor comprises a planar spiral formed of a continuous, conductive,spiral trace extending between bonding pads that is deposited as a layerof the IC chip substrate, the spiral trace and bonding pads consist of ahigh conductivity conductor selected from the group consisting of gold,copper and aluminum-copper metallization to reduce trace height andwidth to thereby reduce parasitic capacitances between adjacent turns ofthe trace and through the IC chip substrate to the ground plane.
 4. Theimplantable medical device of claim 3, wherein the spiral trace andbonding pads consist of a high conductivity conductor selected from thegroup consisting of gold, copper and aluminum-copper metallization toreduce trace height and width to thereby reduce parasitic capacitancesbetween adjacent turns of the trace and through the IC chip substrate.5. The implantable medical device of claim 1, wherein the IC chipsubstrate further comprises a ground plane, and the IC inductor isformed of a planar spiral formed of a continuous conductive traceextending between bonding pads that is suspended above and spaced fromsaid ground plane formed by micromachining substrate material betweenthe exposed surface of the suspended planar spiral and the ground planeaway, to thereby reduce parasitic capacitances between adjacent turns ofthe trace and through the IC chip substrate to the ground plane.
 6. Theimplantable medical device of claim 5, wherein the spiral trace andbonding pads consist of a high conductivity conductor selected from thegroup consisting of gold, copper and aluminum-copper metallization toreduce trace height and width to thereby reduce parasitic capacitancesbetween adjacent turns of the trace and through the IC chip substrate.7. The implantable medical device of claim 5, further comprising atleast one discrete capacitor mounted to said exposed IC chip surface. 8.The implantable medical device of claim 1, wherein: said electroniccircuit module comprises an RF module incorporating a telemetrytransceiver comprising an RF module substrate, an IC chip mounted tosaid RF module substrate and at least one IC inductor formed integrallywith said IC chip thereby reducing the form factor of the RF module. 9.The implantable medical device of claim 8, wherein: said RF modulesubstrate includes a predetermined RF module substrate thickness, a wellformed in said RF module substrate extending from an RF module substratesurface through at least a portion of said RF module substratethickness, and at least one module bonding pad formed on the RF modulesubstrate surface; said IC chip includes predetermined IC chip substratethickness, is mounted within said well of said RF module substratethereby reducing the form factor of the RF module, and has at least oneIC bonding pad formed on an exposed IC chip surface; and a conductorextending between said module bonding pad and said IC bonding pad. 10.An implantable medical device operable to perform a therapeutic and/ormonitoring function comprising: a housing having a housing side wall andinner and outer wall surfaces of a predetermined contour enclosing ahermetically sealed chamber: and a battery enclosed within saidhermetically sealed chamber; and an electronic circuit module powered bythe battery comprising a plurality of discrete components and at leastone integrated circuit IC chip mounted to a circuit board having avolumetric form factor dimensioned to fit within said hermeticallysealed chamber along with said battery, said electronic circuit modulecomprising at least one IC inductor formed integrally with said IC chipthereby reducing the form factor of the electronic circuit module;wherein the IC inductor comprises a planar spiral formed of acontinuous, conductive, spiral trace extending between bonding pads thatis deposited as a layer of the IC chip substrate, the spiral tracehaving turning points that are angled at less than 90° to reduceparasitic capacitance between adjacent turning points of the spiraltrace, and wherein the spiral trace and bonding pads consist of a highconductivity conductor selected from the group consisting of gold,copper and aluminum-copper metallization to reduce trace height andwidth to thereby reduce parasitic capacitances between adjacent turns ofthe trace and through the IC chip substrate.
 11. The implantable medicaldevice of claim 10, wherein the IC chip substrate further comprises aground plane spaced from said planar spiral, and said continuousconductive trace extending between the bonding pads is deposited over anexposed surface of a suspended platform of the IC chip substrate formedby micromachining substrate material between the exposed surface of thesuspended platform and the ground plane away, to thereby reduceparasitic capacitances between adjacent turns of the trace through theIC chip substrate to the ground plane.
 12. An implantable medical deviceoperable to perform a therapeutic and/or monitoring function comprising:a housing having a housing side wall and inner and outer wall surfacesof a predetermined contour enclosing a hermetically sealed chamber; anda battery enclosed within said hermetically sealed chamber; and anelectronic circuit module powered by the battery comprising a pluralityof discrete components and at least one integrated circuit IC chipmounted to a circuit board having a volumetric form factor dimensionedto fit within said hermetically sealed chamber along with said battery,said electronic circuit module comprising at least one IC inductorformed integrally with said IC chip thereby reducing the form factor ofthe electronic circuit module; wherein the IC inductor is formed of aplanar spiral formed of a continuous conductive trace extending betweenbonding pads that is deposited as a layer of the RF IC chip substrate,the IC chip substrate further comprises a ground plane spaced from saidplanar spiral, and said continuous conductive trace extending betweenthe bonding pads is deposited over an exposed surface of a suspendedplatform of the IC chip substrate formed by micromachining substratematerial between the exposed surface of the suspended platform and theground plane away, to thereby reduce parasitic capacitances betweenadjacent turns of the trace through the IC chip substrate to the groundplane.
 13. The implantable medical device of claim 12, wherein thespiral trace and bonding pads consist of a high conductivity conductorselected from the group consisting of gold, copper and aluminum-coppermetallization to reduce trace height and width to thereby reduceparasitic capacitances between adjacent turns of the trace and throughthe IC chip substrate.
 14. An implantable medical device operable toperform a therapeutic and/or monitoring function comprising: a housinghaving a housing side wall and inner and outer wall surfaces of apredetermined contour enclosing a hermetically sealed chamber; and abattery enclosed within said hermetically sealed chamber; and anelectronic circuit module powered by the battery comprising a pluralityof discrete components and at least one integrated circuit IC chipmounted to a circuit board having a volumetric form factor dimensionedto fit within said hermetically sealed chamber along with said battery,said electronic circuit module comprising at least one IC inductorformed integrally with said IC chip thereby reducing the form factor ofthe electronic circuit module; said electronic circuit module comprisingan RF module incorporating a telemetry transceiver comprising an RFmodule substrate, an IC chip mounted to said RF module substrate and atleast one IC inductor formed integrally with said IC chip therebyreducing the form factor of the RF module; said RF module substrateincluding a predetermined RF module substrate thickness, a well formedin said RF module substrate extending from an RF module substratesurface through at least a portion of said RF module substratethickness, and at least one module bonding pad formed on the RF modulesubstrate surface; said IC chip having a predetermined IC chip substratethickness and being mounted within said well of said RF module substratethereby reducing the form factor of the RF module, and having at leastone IC bonding pad formed on an exposed IC chip surface; a conductorextending between said module bonding pad and said IC bonding pad; andat least one discrete capacitor mounted to said exposed IC chip surface.